1. Field of the Invention
The present invention relates to an ink-jet printer and an ink tank for use in the inkjet printer, wherein the ink tank includes a foam for absorbing and holding ink.
2. Related Art
There is a related art foam-type ink tank used for an ink-jet printer. The foam-type ink tank has a foam containing portion for containing a foam which is used for absorbing and holding ink, an ink outlet that communicates with the foam containing portion, and ports communicating with the atmosphere for opening the foam containing portion into the atmosphere. When ink is sucked under the discharge pressure of an ink-jet head, air corresponding to the sucked amount of ink is caused to flow into the foam containing portion.
In the case of such a foam-type ink tank, a mechanism for detecting the presence or absence of ink in the ink tank in which ink is directly stored, for example, an optical sensor utilizing a prism reflective surface that returns light to the original reflective surface in the absence of ink, or a detection mechanism using a sensor utilizing a change in impedance originating from the presence or absence of ink across a pair of electrodes cannot be directly used to detect the presence or absence of ink.
Consequently, an ink end has heretofore been detected as the result of calculation of the used amount of ink according to the number of dots of ink discharged from the ink-jet head and the sucked amount of ink by an ink pump for sucking ink from the ink-jet head.
Incidentally, a condition in which ink in the ink tank has almost run out is generally called a ‘real end’ and a condition in which the remaining ink in the ink tank has decreased to a predetermined amount or smaller is also generally called a ‘near end.’ However, the ‘ink end’ used in this specification includes both of these conditions unless otherwise specified.
The method of detecting the ink end by detecting the running-out of ink by calculating the used amount of ink and the like has the following problems. Since the discharged amount of ink from the ink-jet head and the sucked amount of ink by means of the ink pump undergo wide variation, the used amount of ink that has been calculated according to these quantities also shows a variation far greater than that of the amount of ink actually used. Therefore, a great margin is usually set in order to settle the ink end. Consequently, a greater amount of ink may be left at a point of time when the ink end is detected, whereby ink may often be wasted.